This invention relates generally to derrick cranes for loading and unloading cargo, particularly in marine cargo-handling work. More particularly, the invention relates to an improved derrick crane having a derrick boom which can be revolved through 360 degrees either clockwise or counterclockwise from a central position without mutual contacting and rubbing of derricking and hoisting wire cables, and which can be positively driven or held without play due to causes such as gear backlash.
Deck cranes for marine use are most highly developed laborsaving cargo-handling gears but have heretofore been accompanied by the following problems. Since all components of the crane equipment revolve together with the hoisted cargo, the weight of the revolving parts is extremely heavy, and, in the case where deck cranes are installed on a ship, the center of gravity of the ship becomes high, whereby the ship stability is reduced. Furthermore, these cranes are ordinarily limited to maximum load capacity of 30 metric tons at present and possibly 50 metric tons in the future.